Human skin coloration, mouse coat color patterning, and pigmentation in all mammals provide striking demonstrations of how genes control the development and overall appearance of organisms. In mammals, all pigmentation results from the production of melanin in the melanocyte cells found in the hair and skin. While hair pigmentation, which is responsible for mouse coat color, has been well studied genetically and biochemically, the regulation of skin pigmentation, important for human coloration, has been less clear. Recently, a subset of mouse pigmentation mutants have been identified that affect the skin, but have little or no effect on hair skin pigmentation and to define the mechanism of melanocyte cell fate determination. Using these mutants as a tool, I propose to combine in vivo studies with genome wide molecular expression studies to dissect the mechanisms that differentially regulate hair and skin pigment cells. By analogy to previous work with mouse hair color mutations, these studies may also uncover general principles that control cell migration, signaling, and differentiation.